High viscosity dispersions of rubbery materials



Patented Dec. 25, 1951 UNITED STATES T r OFFECB\ HIGH VISCOSITY DISPERSIONS OF RUBBERY MATERIALS Robert E. Mun sell, Morris Plains, N. '.I., assignor to ThePatent and. Licensing Corporation, New York, N.'Y.; a corporation of Massachusetts No.Drawing.. Application J uly, 3, 1948, Serial No. 37,080

4 Claims. (Cl. 260-8) In the commercial utilization of aqueous dis-.

persions of rubbery material it is irequently necessary to employ a dispersion having a rela tively high viscosity When, for example, it is desired .to apply a dispersionas a coating by means of a spreader or similar deviceit is frequently necessary to employ a dispersion having a viscosity in the range of 70,000 to 100,000 centipoises in .order properlyvto perforrnthis opera tion. For other commercial applications, viscosities of the order of 10,000 to 18,000centipoises are commonly required. Various materials have. been proposed for additionto rubbery dispersions to increase viscosity as, for example, alkali metal hydroxide caseinates, formed by dissolving casein in alkali metal hydroxide solutions. While increased viscosity hasthus been realized. it has been found that dispersions treated in this manner rapidly decrease in viscosity upon standing, that is to say, they lack viscosity stability. This is of course disadvantageous, since a dispersion which may have satisfactory viscosity when shipped by the producer will have so changed in viscosity during transit that; when it arrives at the consumers plant,it'-;is unsatisfactory for use without special treatment. Further, it has been found that, in thecase of dispersions of relatively high pH, i. e. 1 0.5 or above, alkali metal hydroxide caseinates and similar thickening agents have very littleviscosity-increasing action. e

It is an object of this invention to provide diss persions of rubbery-material having good :vis.'

cosity stability.

It is a further object of this invention to pro-- vide a process for increasing substantially the viscosity of dispersions of relatively highv pI-l'.

Other objects and features .of the invention will be. apparent from. the description which fol-1 lows.

According. toqthe invention, viscous dispersions of good viscosity stability may, be. prepared by incorporating in a dispersion of rubbery material .a small quantity of a thickening agent vention are borax, sodium carbonate, sodium.

silicate and trisodium phosphate. The combination of casein and an alkaline buffer salt, when incorporated even in small amounts in an aqueous dispersion of rubbery material, effects a sharp increase in the viscosity of the dispersion and imparts to the dispersion good viscosity stability whereby the viscosity is maintained for a relatively long period of time, compared with stability periods attainable with alkali metal hydroxide caseinates and like thickening agents. Further, a stable, high viscosity may thus be imparted to'a dispersion of rubbery material even though the dispersion has a relatively high alkalinity, i. e., a pHof 10.5 to 12. In the case-of dispersions of lower alkalinity, i. e., below about pH 10, forwhich alkali metal caseinates are to some extent satisfactory; in so far as increasing viscosity is concerned, I have found that by employing my casein-alkalinev buffer salt agent, in accordance with the invention, a substantially greater increase in viscosity is realized .for a given quantity of thickening .agent.

My invention is applicable, bothto dispersions of natural rubber and to dispersions of so-called synthetic rubbers, such as neoprene (polymerized Z-chlorobutadiene-lB) and butadiene-styrene eopolymer,known in one commercial form as GR-S. The rubbery. dispersions ,may be in the form of latices or may be artificial dispersions, such as reclaim dispersions. The advantages of my invention are particularly notice-- able in the case of artificial dispersions in which alkali metal soaps, e. g., sodium or potassium soaps of oleic acid or tall oil, are employed as the dispersing agent,,although the invention; is not limited thereto.

The alkaline buffer salt and casein are pref-1 erably incorporated in the dispersions in an aqueous medium. Thev aqueous casein-alkaline buffer salt agentmay be prepared, forexample,

by swelling the casein inwater. and then adding the alkaline buffer salt. tothe casein slurry.

Theaqueous solution preferably contains suiii-h cient-Water to provide maximum ease of handling and mixing andto provide, at the same properties.

ticularly advantageous to incorporate at least a part of the casein and alkaline. buffer salt.

during the preparation of the dispersion. It

is also desirable to incorporate some of the casein.

and alkaline buffer salt during the compounding of latices. All of the casein-buifer salt thickening agent may, however, be successfully incorporated in the finished dispersions, whether an artificial dispersion or a natural or synthetic rubber latex. In the case of a dispersion in which the casein-buifer salt agent has been incorporated during the preparation thereof, additional quantities of my thickening agent may be readily added to the completed dispersion to adjust the viscosity to any desired value.

Significant increases in viscosity are obtainable with relatively small quantities of my casein-buffer salt thickening agent. I have found, for example, that as little as 0.5-l.5% casein and 0.1-0.3% buifer salt, based on the dry weight of the rubbery material in the dispersion, when incorporated in a dispersion having a viscosity of say, 2000-3000 centipoises raises the viscosity of the dispersion to about 15,00018,000 centipoises and imparts to the dispersion good viscosity stability. The quantity of casein-buffer salt thickening agent incorporated in the dispersion will, of course, depend upon the ultimate viscosity desired. Increased quantities result in higher viscosities. I have found that the viscosity stabilizing effect of the casein-buffer salt agent is effective even at exceedingly high viscosities, i. e. of the order of '70,000-l00,000 centipoises. Such viscosities which are frequently required for dispersions for use as spreader pastes may be obtained byv incorporating in the dispersion relatively small amounts of casein and of alkaline bufier salt. For example, the viscosity of a dispersion of reclaimed rubber may be raised from about 2000-3000 centipoises to about 100,000 centipoises by the total addition of about 3% of casein and about 0.6% of alkaline buffer salt, based on the weight of the reclaimed rubber in the dispersion. When part of the casein-bufier salt agent is added during the dispersing operation, or during the compounding step in the case of latices, it is generally desirable to add only sufficient agent to impart stability to the dispersion and thereby facilitate the dispersing or compounding operations. After dispersing or compounding is completed, the viscosity of the product is readily adjusted to the desired value by the direct addition of further quantities of the casein-alkaline buffer salt agent.

The quantity of agent will vary somewhat depending upon the type of rubbery material as well as the type of compounding ingredients in the dispersion. Latices generally require slightly greater quantities than do artificial dispersions to obtain comparable results. Generally speaking, one part of the alkaline buffer salt is used for each 5 parts of casein although this relationship is subject to variationdepending upon the specific buffer salt. The dispersions of rubbery material which may be employed in accordance with the invention may be prepared in any known manner and the" invention is not'limitedto dispersions prepared in accordance with any particular process. Artie ficial dispersions are generally prepared by incorporating a dispersing agent, such as an'alkali metal soap, into previously plasticized rubbery material, and then masticating the batch with gradual continued addition of water until therev is brought about an inversion of phase; 1. e., the water becomes the continuous phase and the rubbery material becomes the discontinuous or dispersed phase. Plasticizing agents, fillers and the like are commonly incorporated, during the dis-.

persing operation to facilitate dispersion and to impart desirable properties to the compound. It is advantageous to incorporate a portion of the casein-buffer salt agent during the preparation of the dispersion to gain the advantage of the dispersing and stabilizing properties of the casein.

The following examples-are illustrative of the invention, all parts being by weight.

Example 1 One hundred parts of reclaimed rubber, in the form of digester tube reclaim, were worked for about three minutes in a Banbury. At the end of this time the temperature of the rubber was in the range of 250 to 300 F. The Banburyed rubber was added to an internal mixer of the Werner-Pfieiderer type, together with 25 parts of whiting, 8 parts of tall oil, 20 parts of coumaroneindene resin, 2 parts of zinc oxide, 1 part of Agerite Stalite and 0.2 part of Dowicide A and the mass mixed for fifteen minutes. During the mixing operation 2 parts of sulphur and 8.33 parts of water were added, whereupon 4 parts of an aqueous solution of alkali such as a 45% solution of potassium hydroxide were added. Preferably the alkali solution is added in several increments. After a few minutes of further mixing, with gradual addition of further quantities of water, inversion of phase occurred. Substantially immediately following inversion, 3.2 parts of an aqueous solution of casein and borax were added, said solution being composed of approximately 15% casein, 3% borax, 0.2% Dowicide A, and 81.8% water. The dispersion was then diluted to a solids content of about 70% by the gradual ad-- dition of a 0.2% solution of KOH-tall oil soap in water.

The viscosity of the thus-prepared dispersionwas determined and a small additional amount of the casein-borax solution was added to raise the viscosity to l5,000-18,000 centipoises. This required less than 6 parts of the casein-borax solution. The viscosity was found to be substantially unchanged when tested after 20 days. Higher viscosities are readily obtainable by incorporating additional quantities of the casein-borax solution. For example, a further addition of 2% casein and 0.4% borax, based on the weight of the reclaimed rubber, raises the viscosity of the thus-prepared dispersion to about 100,000 centipoises.

The various compounding agents are those commonly employed in the preparation of rubbery dispersions. The coumarone-indene resin is employed as a plasticizer for the reclaim. Whiting is a filler, zinc oxide functions as a curing agent, and Agerite Stallte is a' proprietary anti-oxidant composed essentially of heptylated diphenylamine. Sulphur is the vulcanizing' agent. Dowicide A' is a proprietary preservative agent for the casein and is, chemically, sodium ortho Example 2 This example shows the use of my casein-buffer salt agent to increase the viscosity of a latex compound.

Commonly employed compounding ingredients;

betanaphtholQ for example, I

were added to 334 parts of GR-S latex X359 and the following latex compound obtained.

Ingredients Composition Parts GR-S latex X359 (60% solids) KOH solution 57.5% clay slurry 50% Agerite Powder past 50% sulphur paste.

To 231 parts of the above GR-S latex compound Were added 13.3 parts of a casein-borax solution casein, 3% borax, 0.4% Dowicide A and 81.6% water). The quantities employed are equivalent to 2% casein and 0.4% borax, based on the weight of GR-S in the latex compound. Agerite Powder is a proprietary antioxidant composed of phenyl-beta-naphthylamine.

The resulting product had a pH of 10.4 and a viscosity of 42,000 centipoises, as determined with a Brookfield viscosimeter.

Since certain changes may be made in the invention without departing from the scope thereof, as defined in the appended claims, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A viscous rubbery dispersion having a vis cosity of at least 10,000 centipoises and comprising a rubbery material from the group consisting of natural rubber, polymerized 2-chlorobutadione-1,3 and butadiene styrene copolymers dispersed in an aqueous medium, said dispersion consisting predominantly of solids, the rubbery material representing the major proportion of the solids, and containing from .5% to 3% of casein and from .1% to .6% of an alkaline bufier salt based on the weight Of the rubbery material and being characterized by good viscosity stability, the viscosity of said dispersion remaining substantially unchanged over a period of several days.

2. A viscous rubbery dispersion having a viscosity of at least 10,000 centipoises and comprising a rubbery material from the group consisting of natural rubber, polymerized Z-chlorobutadiene-1,3 and butadiene styrene copolymers dispersed in an aqueous medium, said dispersion consisting predominantly of solids, the rubbery material representing the major proportion of the solids, and containing from .5% to 3% of casein and from .1% to .6% borax based on the weight of the rubbery material and being characterized' by good viscosity stability, the viscosity of said dispersion remaining substantially unchanged over a period of several days.

3. A viscous rubbery dispersion having a viscosity between 10,000 and 100,000 centipoises of a rubbery material from the group consisting of natural rubber, polymerized Z-chlorobutadiene- 1,3 and butadiene styrene copolymers dispersed in an aqueous medium, said dispersion consisting predominantly of solids, the rubbery material representing the major proportion of the solids, and containing from .5% to 3% of casein and from .1% to .6% of borax based on the weight of the rubbery material and being characterized by good viscosity stability, the viscosity of said clispersion remaining substantially unchanged over a period of several days.

4. A method of imparting a stable viscosity of 10,000 to 100,000 centipoises to an aqueous dispersion of a rubbery material selected from the group consisting of natural rubber, polymerized 2-chlorobutadiene-1,3 and butadiene styrene copolymers dispersed in an aqueous medium, said dispersion consisting predominantly of solids, the rubbery material representing the major proportion of the solids and the viscosity of said dispersion remaining substantially unchanged over a period of several days, which method comprises incorporating in said dispersion from .5% to 3% of casein and from .1% to .6% of borax based on the weight of the rubbery material.

ROBERT E. MUNSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Dow Chemical (30., Dow Latex 512, copyright 1946, pp. 7 to 9. 

1. A VISCOUS RUBBERY DISPERSION HAVING A VISCOSITY OF AT LEAST 10,000 CENTIPOISES AND COMPRISING A RUBBERY MATERIAL FROM THE GROUP CONSISTING OF NATURAL RUBBER, POLYMERIZED 2-CHLOROBUTADIENE-1,3 AND BUTADIENE STYRENE COPOLYMERS DISPERSED IN AN AQUEOUS MEDIUM, SAID DISPERSION CONSISTING PREDOMINANTLY OF SOLIDS, THE RUBBERY MATERIAL REPRESENTING THE MAJOR PROPORTION OF THE SOLIDS, AND CONTAINING FROM .5% TO 3% OF CASEIN AND FROM .1% TO .6% OF AN ALKALINE BUFFER SALT BASED ON THE WEIGHT OF THE RUBBERY MATERIAL AND BEING CHARACTERIZED BY GOOD VISCOSITY STABILITY, THE VISCOSITY OF SAID DISPERSION REMAINING SUBSTANTIALLY UNCHANGED OVER A PERIOD OF SEVERAL DAYS. 